Bushing-type mountings are widely known in the art. One such mounting is described in the commonly assigned U.S. Pat. No. 3,895,408 to Leingang, the disclosure of which is hereby incorporated by reference herein. This type of mounting 10 is typically referred to as a "center-bonded mounting" and includes a rigid cylindrical sleeve 14 which is usually bonded to a round cross-section, concentric elastomer section. The elastomer section includes a body portion 11 and opposite end portions 12 and 13. End portions 12 and 13 generally determine the as-installed axial spring rate, while the body portion 11 generally determines the radial spring rate.
This type of mount, referred to as a "CB Series" center-bonded mount is manufactured by Lord Corporation of Erie, Pa. These mounts isolate vibration, absorb shock loads, and attenuate noise due to structureborne vibration. CB mounts are available in a number of standard sizes, and thus are highly cost effective. One of the keys to keeping the cost low is the round cross-section used in the CB mounting concept. This round cross-section leads to low mold costs because it simplifies the machining practices required to produce the molds for bonding these mounts.
The mounts are installed by first inserting the CB mounting through a circular receiving bore. Second, flat washers or the like are placed on the upper and lower sides of the mounting. The assembly is then precompressed by tightening the attachment bolt against the inner member. However, one of the drawbacks of prior mounting systems and assemblies using center-bonded mounts was the inability to exhibit differing radial spring rates, a requirement for some systems. Thus, for systems requiring differing spring rates, more complex mounting systems and bonded components were required. In other words, because of the round cross-section of the center-bonded mount required for low manufacturing cost and standardization, the center-bonded mounts were thought to be capable of only one common radial spring rate. U.S. Pat. No. 3,128,999 to Schmitt, which is commonly assigned, and U.S. Pat. No. 3,675,881 to Caldwell, describe other center-bonded mount embodiments and the disclosures of each is hereby incorporated by reference herein.